Surface treatment of magnesium metal articles



0a. 17, 1961 H. J. PALUMBO 3, 0

SURFACE TREATMENT OF MAGNESIUM METAL ARTICLES Filed Aug. 28, 1959 SURFACE COATWG MAGNESIUM METAL INVENTOR. HENRY 3. PALuMbo ATTORNEY United States Patent all-84,869 SURFACE TREATMENT OF MAGNESIUM METAL ARTICLES Henry J. Palumbo, Somerville, N.J., assignor to Johns- Manville Corporation, New York, N.Y., a corporation of New York Filed Aug. 28, 1959, Ser. No. 836,605 8 Claims. (Cl. 117-46) This invention relates to the surface treatment of magnesium metal articles to produce a corrosion-resistant protective surface coating thereon and to corrosion-resistant magnesium metal articles produced by such treatments.

Magnesium metal is relatively reactive and corrodes quite easily. Conditions encountered at seashore areas or other places where salt water may be present are particularly troublesome as far as corrosion of magnesium metal is concerned.

This corrosion problem can be mitigated to some extent by alloying magnesium metals with small amounts of other metals, but with alloys containing a major portion of magnesium metal, the corrosion problem is always very great. Accordingly, manufacturers and fabricators of magnesium metal and light-weight magnesium metal alloys have been arduously searching for commercially feasible methods for protectin the surface of magnesium metal articles against corrosion.

A principal object of this invention is the provision of new methods of protecting magnesium metal surfaces against corrosion. Further objects include:

(1) The provision of new processes for the surface treatment of magnesium metal articles to produce a corrosion-resistant protective surface coating thereon.

(2) The provision of new forms of magnesium metal surfaces having bluish gray to black colored corrosionresistant coatings thereon to protect the surface of the metal against the corrosive efiects of atmospheric conditions, salt water or the like.

(3) The provision of methods for providing magnesium metal articles with corrosion protective surfaces which may be conducted without need for special handling or processing equipment, using relatively inexpensive and readily obtainable treating materials.

Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed descritpion, while indicating preferred embodiments of the invention, is given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

These objects are accomplished according to the present invention by processes which broadly involve contacting the surface to be treated of a magnesium metal article with a hydroxy compound, selected from the group consisting of glycols, carbohydrates, and hydroxyl group containing ethers thereof, heating the article while in contact with the hydroxy compound for at least about one hour at a temperature above about 150 F. and thereafter removing the compound from contact with the article. As a result of such operations, there is formed on the treated surface of the magnesium metal, a visible coating which varies in color from light bluish gray to black, and in appearance from a relatively flat 3,004,869 Patented Oct. 17, 1961 matte to a bright lustre, such coating providing corrosion resistance to the magnesium metals under fairly severe conditions of humidity, exposure to aqueous media containing sodium chloride, or other conditions which would readily corrode untreated magnesium metal.

in the preferred methods of the invention, the protective surface coating on the magnesium articles is formed by first providing a substantially anhydrous mixture comprising an oil selected from the group consisting of hydrocarbon oils and fatty acid ester oils, plus a hydroxy compound as just mentioned, covering the surface to be treated of the magnesium metal article with a layerof the liquid mixture, e.g., by immersing the metal article in a bath of the liquid mixture, maintaining the article in contact with the liquid layer for at least about one hour at a temperature of between about and 350.F., and subsequently removing the liquid mixture fromthe metal surface.

The accompanying drawing is a perspective view of a piece of magnesium metal with a portion thereof provided with the corrosion-resistant protective surface covering of this invention.

A more complete understanding of the new processes and resulting products of this invention may be obtained from consideration of the following actual examples of surface treatment operations conducted in accordance with the invention.

EXAMPLE 1 A group of rectangular coupons measuring approximately 1" x 2" are cut from /8" bar stock of magnesium metal. Three of these coupons are suspended on a rack inside a glass beaker so that only several points along one of the side edges of each coupon are in contact with any supporting surface. A mixture of castor oil con,- taining very short fiock particles of alpha cellulose (10% by weight) is then poured into the beaker until the metal coupons are totally covered by the liquid mixture. The beaker and its contents are then placed on a hot plate and the liquid mixture is heated up to a temperature of 250 F. At the end of one hour, during which time the castor oil mixture is maintained at 250 F., the metal coupons are removed from the oil bath and are washed with ethyl alcohol and then dried. V

The resulting coupons have a coating thereon which appears to be completely smoothand uniform, grayish black in color, and quite lustrous. To the touch, the resulting coating feels waxy, similar to a freshly waxed surface of a piece of furniture. The coating is tenaciously held to the metal surface and cannot be removed by vigorous bufiing or polishing of the surface. Moreover, the metal surface may be peened, bent, drawn or similarly worked without any apparent damage to the coating. On the other hand, the coating may be removed by scratching the metal surface with a sharp instrument or the like. The coating is about 1 mil in thickness.

The three coupons are placed upon a supporting surface and a piece of filter paper saturated with a 10% solution of sodium chloride is placed on the surface of one of the coupons. On a second of the coupons, there is placed a piece of moist asbestos paper, while the third coupon is left uncovered. Three additional coupons as cut from the bar stock, but left untreated, are placed on the supporting surface adjacent to the three treated coupons. One of these is covered with filter paper saturated with the salt solution, the second is covered with apiece of moist asbestos paper, and the third is left uncovered. A bell jar is then placed over the six coupons to maintain them in an atmosphere of substantially 100% relative humidity. The coupons are kept in this fashion for one week at approximately 70 F. At the end of this time, the bell jar is removed, the filter paper and asbestos paper are taken off the coupons, and the six coupons are visually inspected. Aside from a slight deposit of salt crystals on one of the black coated coupons, the three treated coupons appear to be in substantially the same condition as when first placed under the bell jar, i.e., their coated surfaces remain smooth and lustrous. In contrast, the surfaces of the untreated coupons which were in contact with the salted filter paper and the asbestos paper are both severely pitted, some of the pits extending as much as %2" into the body of the metal. The remaining untreated coupon does not appear as severely corroded as the other two untreated coupons but, it is noticeably difierent from its appearance before the beginning of the corrosion test, and has a dull, somewhat chalky appearance and contains a number of tiny pits.

' EXAMPLE 2 Magnesium metal coupons as described in Example 1 are subjected to surface treatments using twelve difierent treating mixtures to produce corrosion-resistant protective surface coatings on the coupons. Each separate coupon is treated with one of the twelve different treating mixtures which consist of an anhydrous liquid with a boiling point above 300 F., having suspended therein particles of carbohydrate material, such particles constituting approximately 10% by weight of the treating mixture. Each of the separate coupons is totally immersed in its respective treating mixture and maintained at an elevated temperature for a sufiicient length of time at least to produce on the exposed surfaces of the coupen, a gr yish-black,1smcoth,;uniform, lustrous coating similar to the coating described in connection with Example 1.

' The resulting coated coupons are tested for corrosion resistance by placing moist asbestos paper in contact with a su'rfaceof the coated coupon, and permitting the paper and coupon to remain in contact for one week. None of the coupons are found to have any visible pitting or other corrosion of the surface which had remained in contact with the asbestos paper. In contrast, an uncoated coupon in contact with moist asbestos paper for one week is found to be severely corroded and to have numerous deep pittings in the-surface which was in contact with the asbestos paper, since moist asbestos pape is highly corrosive to uncoated magnesium metal.

The following table lists the twelve difierent treating mixtures, the .temperatures and time of treatment of the individual test coupons asdescribed above:

Table I Treating Mixture Time Temperature 9F.

(1) ASTM No, 3 oiland flock 1 week.-. 250 (2) ASTM No. 1 oil and flock 20 hours.-- 250 (3) cylinder oil and flock do 250 (4) linseed oil and'flock 3 days.-- 250 (5) ethylene glycol and flock 24 hours..- 250 (6) polyethylene glycol and fie 3 days 250 (7) castor oil and flock 1 hour 250 (8) castor oil and flock", .do 250 (9) castor oil and flock 70 hours, 150 (10) ASTM No. 1 oil and filter paper 1 wee-kl 250 (11) ASTM No. 1 oil and rag pulp- ;do. 250 (12) cylinder 011 and pearl starch--- 2 lio urshi- 250 In the above and following tables, the designated materials may be furtheridentified 13S follows: I

AS N 1 oil i a iscous Pe oleum been 9 9? high aniline point, i.e., relatively saturated.

ASTM N0. 3 oil is petroleum base oil less viscous than No. 1 oil and with a low aniline point.

The flock consisted of very short fibers of alpha cellulose.

EXAMPLE 3 Magnesium metal coupons of the kind described in Example 1 are subjected to treatment with nine different treating materials to determine if, and to what extent, these treating materials produce protective coatings on metal surfaces. Four of the treating materials are single chemical substances, while five of the treating materials are mixtures of chemical substances with a high boiling oil. The treating materials which consist of a mixture of oil and other substance, contain 90% by weight of oil and 10% by weight of the other component. A sin gle coupon is treated in only one of the nine separate treating materials by being totally immersed in the treating material for a periodof 24 hours and at a temperature of 250 F. At the end of the treating operation, the metal coupon is removed from the liquid" treating bath, washed with ethyl alcohol, dried and then inspected to determine if, and to what extent, a protective coating has formed upon the coupon.

Tab e 2 Treating Material Description of Treated Surface no coating; metal presented an etched,

mottled surface.

speckled'light' and darl; areas, no coat g.

l t P 1 f 195W Pa t n coating. grayish blaclglustrous uniform coating.

A. glycerin B. glycerin and ASI M No. 1

D. ethylene glyoolend ASTM E. turtural surface blotehed with tarry deposits;

' no coating." l F. furglral and ASTM No. 1 Do.

0 G. "Tween #80 very light; bluish gray, thin, matte,

uniform coating.

dark bluish gray, un form, lustrous coating appreciably'heavier than with item G.

dark bluish gray, uniform, lustrous coating.

H. Tween #30" and ASTM No. 1 oil.

I. castor oil and-flock In the abovetable, Tween #80 refers to a brand of polyoxyethylene-sorbitan mono-oleate sold by Atlas Powder Co. of Wilmington, Delaware.

- Theresults reported in Table 2 show that glycerin and furfural, either alone or in admixture with a high boiling oil, do not produce a corrosion-resistant protective surface coating on magnesium metal, in contrast to the other treating materials listed in Table 2.

The exact nature of the novel protective coatings for magnesium metal .as provided by this invention has not been determined. Regardless of what the chemical composition of the protective coatings maybe, it has been found that such coatings are formed on magnesium metal when -a surface thereof is in contact with an organic hydroxy compound selected from the group conthe group consisting of hydrocarbon oils and fatty acid ester oils. The proportions of ingredients used in such mixtures should be chosen to provide a mixture of liquid consistency, and may contain between about to 90% by weight of the oil, with the remainder of the mixture being the hydroxy compound.

Total immersion of the magnesium metal article to be treated in a liquid treating bath is the preferred method to be used in forming the protective surfaces of the invention. Such a procedure is readily adapted to large scale commercial operations. However, there are other methods for contacting the surface to be protected of the magnesium metal article with the anhydrous liquid treating material, e.g., by spraying the treating material onto the metal surface.

Specific examples of glycols which may be used in the new treating operations include ethylene glycol; propylene glycol; butandiol-1,4; butandiol-2.,3; a-butylene glycol; fi-butylene glycol; hexandiol-2,3 and the like.

Specific examples of usable carbohydrates include cellulose, starch, dextn'n, sucrose, rag pulp, cotton fibers, wood pulp, paper shreds, arabinose, arabinulose, xylose, dextrose, galactose, mannose, levulose, sorbose, lactose, and ground wood.

Specific examples of usable glycol ethers include diethylene glycol; polyethylene glycol; dipropyleue glycol; diethylene glycol monobutyl ether; diethylene glycol monomethyl ether; polyethylene glycol monoethyl ether; propylene glycol monobutyl ether; u-butylene glycol monohexyl ether; polyethylene glycol monoctyl ether; ,B-butylene glycol monomethyl ether; polyoxyethylene soroitan monoleate; polyoxyethylene sorbitan monostearate and the like.

Specific examples of usable carbohydrate ethers include ethyl cellulose, methyl cellulose; dextrose diethyl ether; mannose monoethyl ether; benzyl cellulose; sorbose trimethyl ether; sucrose monobutyl ether and the like.

Specific examples of usable hydrocarbon oils include cylinder oil; AS'IM No. 1 oil; ASTM No. 3 oil; medicinal white oil; petroleum lubricating oil; diesel fuel and the like.

Specific examples of fatty acid ester oils include castor oil; cotton seed oil; cod liver oil; corn oil; peanut oil; lard oil; menhaden oil; olive oil; herring oil and the like.

The period of time during which the magnesium metal article is in contact with the heated treating material should be suflicient to form on the metal surface a smooth, uniform coating of appreciable thickness, e.g., about 1 mil or more. The novel coatings form faster at the higher temperatures of treatment. Thus, a satisfactory coating may be formed with a particular treating mixture in one hour at 250 F., whereas with the same mixture at 150 F., 10 hours or more may be required to form a suitable coating. A temperature of at least 150 is preferred. The upper range of treatment temperature is not critical, but for practical reasons should be maintained below the boiling point or decomposition temperature of the anhydrous liquid treating material. An upper temperature of 350 is recommended.

The deposition of the protective coating seems to be somewhat self-controlled. Thus, no problem has been experienced in allowing the metal to remain in contact with the heated treating material for very long periods of time, since when a smooth, uniform surface coating is formed, this appears to protect the metal against any tendency to form too thick a coating. Obviously, from the viewpoint of conservation of heat and time, it is not desirable to extend the treating operation beyond the time required to form on the metal surface a smooth, uniform, protective coating.

The surface treating operations of the invention appear to be applicable to all known light metal magnesium alloys, as well as magnesium metal per se, i.e., magnesium metal alloys containing at least 50% by weight of magnesium, and especially those containing 80% or more magnesium by weight. Specific examples of magnesium metal alloys to'which the corrosion-resistant protective surface coatings of the invention may be applied by the described surface treatment operations include American Metal Standards alloys Serial Nos. 3095; 7311; 73.12; 7419; 10,136; 11,332; 11,333; 11,334; 12,842; 12,956; 12,957; 17,514 and 17,515.

Having provided a complete description of the invention in such manner as to distinguish it from other inventions and from what is old, and having provided a description of the best mode contemplated of carrying out the invention, the scope of patent protection to be granted the invention is defined by the following claims.

I claim:

1. A process for the surface treatment of magnesium metal articles to produce a corrosion-resistant protective surface coating thereon which comprises providing a substantially anhydrous liquid comprising at least about 10% by weight of a hydroxy compound selected from the group consisting of glycols, carbohydrates, and hydroxyl group containing ethers thereof, covering the surface to be treated of the magnesium metal article with a layer of said liquid, maintaining said article in contact with said liquid for at least about 1 hour at a temperature of between about 150 and 350 F. and thereafter removing said liquid mixture from said article.

2. A process as defined in claim 1 wherein said atticle is immersedin a bath of said liquid mixture to cover the article With said mixture layer.

3. A process for the surface treatment of magnesium metal articles to produce a corrosion-resistant protective surface coating thereon which comprises providing a substantially anhydrous mixture comprising about to 10% by weight of an oil selected from the group consisting of hydrocarbon oils and fatty acid ester oils and about 10 to 90% by weight of a hydroxy compound selected from the group consisting of glycols, carbohydrates, and hydroxyl group containing ethers thereof, covering the surface to be treated of the magnesium metal article with a layer of said liquid mixture, maintaining said article in contact with said layer for at least about 1 hour at a temperature of between about and 350 F. and thereafter removing said liquid mixture from said article.

4. A process as defined in claim 3 wherein said mixture is of liquid consistency and contains about 90% by weight of said oil, the remainder of the mixture being the hydroxy compound.

5. A process for the surface treatment of magnesium metal articles to produce a corrosion-resistant protective surface coating thereon which comprises providing a substantially anhydrous mixture comprising about 90 to 10% by weight of a hydrocarbon oil and about 10 to 90% by weight of cellulose, covering the surface to be treated of the magnesium metal article with a layer of said liquid mixture, maintaining said article in conact with said layer for at least about 1 hour at a temperature of between about 150 and 350 F. and thereafter removing said liquid mixture from said article.

6. A process for the surface treatment of magnesium metal articles to produce a corrosion-resistant protective surface coating thereon which comprises providing a substantially anhydrous mixture comprising about 90 to 10% by Weight of castor oil and about 10 to 90% by Weight of cellulose fibers, covering the surface to be treated of the magnesium metal article with a layer of said liquid mixture, maintaining said article in contact with said layer for at least about 1 hour at a temperature of between about 150 and 350 F. and thereafter removing said liquid mixture from said article.

7. A process for the surface treatment of magnesium metal articles to produce a corrosion-resistant protective surface coating thereon which comprises contacting the surface to be treated of the magnesium metal article with a hydroxy compound selected from the group conof glycols, carbohydrates, and hydroxyl group containing ethers thereof, heating s'aid article While in contact with said compound for at least about 1 hours to {tethperattqe of at least about 150? F; and thereafter removing said compound from contact with said article. V V

8. A magnesium metal article having a surface thereof coated with a plu ish gray to black colored corrosion- 'esistapt coating prodliced by the p roces s as defiiied in claim 7.

References Cited in the file 0E this patent UNITED SIAIES PATENTS Anderson Nov. 1, 193$ Zoeller Mar. 9, 1954- Hiler c 1111; 24, 1956 Bach L V Oct. 15, 1957 WrotnoWsKi Mar. 29, 1960 FOREIGN PATENTS Gi eat Britain cf Apt. 20, 1943 

3. A PROCESS FOR THE SURFACE TREATMENT OF MAGNESIUM METAL ARTICLES TO PRODUCE A CORROSION-RESISTANT PROTECTIVE SURFACE COATING THEREON WHICH COMPRISES PROVIDING A SUBSTANTIALLY ANHYDROUS MIXTURE COMPRISING ABOUT 90 TO 10% BY WEIGHT OF AN OIL SELECTED FROM THE GROUP CONSISTING OF HYDROCARBON OILS AND FATTY ACID ESTER OILS AND ABOUT 10 TO 90% BY WEIGHT OF A HYDROXY COMPOUND SELECTED FROM THE GROUP CONSISTING OF GLYCOLS, CARBOHYDRATES, AND HYDROXYL GROUP CONTAINING ETHERS 